Age and Paleoclimatic Significance of Holocene Sand Dunes in Northeastern Colorado

Abstract

Abstract Stabilized parabolic sand dunes are extensive in northeastern Colorado and adjacent southwestern Nebraska and suggest that precipitation was lower when the dunes were formed than it is now. Orientations of the parabolic dunes indicate a paleowind from the northwest. Soils developed on these dunes are Ustic Torripsamments with A/AC/C profiles that have morphological and textural properties similar to soils on stabilized dunes in the Nebraska Sand Hills with maximum-limiting radiocarbon dates of about 3000 B.P.; thus most of the Colorado dunes are thought to be correlative with dunes in the Nebraska Sand Hills. In both areas, dunes were probably stabilized c. 1500 B.P. The regional dune formation interval of 3000–1500 B.P. correlates well with a period of glacier retreat in the Colorado Front Range. Archaeological evidence suggests that humans who were living on the central Great Plains in the late Holocene migrated to locations that were probably more favorable for hunting and gathering. An earlier dry phase is represented by extensive eolian sands that apparently underlie the late Holocene parabolic dunes; where exposed at the surface, these sands have well-developed soils classified as Ustollic Haplargids or Aridic Argiustolls. Some of these older sands may represent the mid-Holocene Altithermal drought. Holocene dune formation from northwesterly winds can best be explained by a strong westerly circulation pattern, with a longer residence time of dry. Pacific-derived air than is the case at present. Sand drift was partially controlled by bedrock topographic barriers and the locations of rivers. Key Words: parabolic dunessoil developmentarchaeologypaleowindsHoloceneColorado Notes 1. The author's current address is U.S. Geological Survey, MS 424, Box 25046, Federal Center, Denver, Colo. 80225